1. Field of the Invention
This invention relates to novel cyanoguanidine derivatives and more particularly to novel cyanoguanidine derivatives which are advantageously usable in various applications such as, for example, an epoxy resin curing agent. This invention also relates to bis-cyanoguanidine type and cyanoguanidine type epoxy resin curing agents advantageously usable for hardening epoxy resins and to a thermosetting resin composition or a photocurable and thermosetting resin composition using the curing agent.
2. Description of the Prior Art
At the soldering step for mounting electronic parts as on the surface of a printed circuit board, the solder mask is used for the purpose of preventing the solder from adhering to impertinent portions and protecting the circuits from the external environment.
In consequence of the increased density of printed circuits in the board and in association with the problem of environmental pollution, the practice of using an alkali development type photocurable and thermosetting resin composition as the material for the solder mask has been popularized. As for the photocurable and thermosetting resin composition developable with an alkali aqueous solution, Kamayachi et al. U.S. Pat. No. 5,009,982 issued on Apr. 23, 1991 discloses a photocurable and thermosetting resin composition containing a photosensitive resin which is obtained by the reaction of a saturated or unsaturated polybasic acid anhydride with a reaction product of a novolak type epoxy compound and an unsaturated monocarboxylic acid and published Japanese Patent Application, KOKAI (Early Publication) No. (hereinafter referred to briefly as "JP-A") 3-289656 discloses a liquid photoimageable solder resist developable with an alkali aqueous solution, which uses a photosensitive resin obtained by the reaction of acrylic acid with a copolymer of an alkyl (meth)acrylate and a glycidyl (meth)acrylate and the subsequent reaction of a polybasic acid anhydride with the resultant reaction product. The alkali development type photocurable and thermosetting resin composition, however, is generally at a disadvantage in lacking storage stability because it is liable to gain in viscosity and form gel with the elapse of time. It is, therefore, marketed generally in the form of a two-component package which consists of a main agent formed mainly of a photosensitive resin and a hardener formed mainly of a thermosetting component. The consumer is expected to mix the main agent with the hardener at the time he makes use of the composition.
Incidentally, in the solder resist, a coating film formed of the photocurable and thermosetting resin composition is exposed to light and developed to produce a prescribed resist pattern and the resist pattern is thermally set by postcuring.
The alkali development type photocurable and thermosetting resin composition mentioned above is so adapted as to produce a solder resist film excelling in adhesiveness, hardness, resistance to heat, electrical insulation properties, or the like by using an epoxy resin, in general, as the thermosetting component and, during the course of the postcuring mentioned above, causing a copolymerization reaction between the carboxyl group in the side chain of the photosensitive resin and the epoxy group in the epoxy resin, in addition to the curing reaction of the thermosetting components. For the purpose of accelerating the reactions mentioned above during the course of the postcuring, an epoxy resin curing agent is generally used in combination with the epoxy resin.
Various compounds have been known as effective curing agents for epoxy resins. Cyanoguanidine (otherwise called "dicyandiamide") is well known as one of the curing agents. If cyanoguanidine is used in combination with an epoxy resin in the alkali development type photocurable and thermosetting resin composition, the mixture of the main agent with the hardener will be at a disadvantage in lacking storage stability and suffering from a short shelf life as a single liquid composition.
It is disclosed in International Publication WO 92/01726 that a substituted cyanoguanidine is useful as a curing agent for an epoxy resin. The invention disclosed in WO 92/01726 proposes to incorporate a specific substituent into cyanoguanidine for the purpose of improving the solubility thereof. Thus, it aims to provide a substituted cyanoguanidine compound which is soluble in various organic solvents.
Generally, a substituted cyanoguanidine compound which exhibits solubility in various organic solvents, however, readily reacts with an epoxy resin at normal room temperature because it also exhibits solubility in a liquid epoxy resin or in an epoxy resin solution. As a result, the photocurable and thermosetting resin composition which contains this substituted cyanoguanidine compound in combination with an epoxy resin has a short shelf life and is deficient in the potential curing property.
Redmon et al. U.S. Pat. No. 2,455,807 issued on Dec. 7, 1948 discloses substituted 3-cyanoguanidines which have aliphatic, aromatic, and heterocyclic substituents. They are claimed to be useful for the preparation of medicines, dyes, insecticides, antioxidants, vulcanization accelerators, plasticizers, resin modifiers, ion-exchange resins, and leather, paper, and textile processing agents. Their use as an epoxy resin curing agent is mentioned nowhere therein.
Compounds which resemble the cyanoguanidine derivatives of the present invention are disclosed in Journal of the Chemical Society, 1956, pp. 4422-4425 and JP-A-64-71,846. Particularly, JP-A-64-71,846 discloses 1,6-di(N.sup.3 -cyano-N.sup.1 -guanidino)hexane which is an intermediate useful for the production of bisbiguanidine and polybiguanidine to be used as disinfectants and biocides and chlorohexidine to be used as anti-fungus agents and antiseptics. The novel cyanoguanidine derivatives which the present invention aims to propose are mentioned nowhere in these publications. Neither is the use of the cyanoguanidine derivatives as an epoxy resin curing agent mentioned anywhere therein.